The pentose phosphate pathway (PPP) is one of the most targeted pathways in metabolic engineering. This pathway is the primary source of NADPH, and it contributes in fungi to the production of many compounds of interest such as polyols, biofuels, carotenoids, or antibiotics. However, the regulatory mechanisms of the PPP are still not fully known. This review provides an insight into the current comprehension of the PPP in fungi and the limitations of this current understanding. It highlights how this knowledge contributes to targeted engineering of the PPP and thus to better performance of industrially used fungal strains. Key points • Type of carbon and nitrogen source as well as oxidative stress influence the PPP. • A complex network of transcription factors regulates the PPP. • Improved understanding of the PPP will allow to increase yields of bioprocesses.
The reduction of sugar intake by adults has been stated by the World Health Organization as an important strategy to reduce the risk of non-communicable diseases. Erythritol is a four-carbon sugar alcohol that is considered as a highly suitable substitution for sucrose. This review article covers approaches for the separate stages of the biotechnological production of erythritol from cultivation to the downstream section. The first part focuses on the cultivation stage and compares the yields of erythritol and arising by-products achieved with different types of substrates (commercial versus alternative ones). The reported numbers obtained with the most prominently used microorganisms in different cultivation methods (batch, fed-batch or continuous) are presented. The second part focuses on the downstream section and covers the applied technologies for cell removal, recovery, purification and concentration of erythritol crystals, namely centrifugation, membrane separation, ion and preparative chromatography, crystallization and drying. The final composition of the culture broth and the preparative chromatography separation performance were identified as critical points in the production of a high-purity erythritol fraction with a minimum amount of losses. During the review, the challenges for a biotechnological production of erythritol in a circular economy context are discussed, in particular regarding the usage of sustainable resources and minimizing waste streams. Key points • Substitution of sucrose by erythritol can be a step towards a healthier society • Biotechnological production of erythritol should follow a circular economy concept • Culture broth composition and preparative chromatography are keys for downstreaming • Substrate, mother liquor and nutrients are challenges for circular economy
The urgency for reducing the dependence on fossil-based materials is increasing the interest in the utilization of renewable feedstocks. Lignocellulosic residual biomass can be used as feedstock to produce chemicals and energy without generating food security problems. Wheat straw (WS) has a clear potential for developing sustainable processes in a circular bioeconomy context. However, the development of processes requires a strategy for utilizing the hemicellulosic, cellulosic, and lignin fractions. This work covers the utilization of the hemicellulosic fraction as the first stage of a wheat straw biorefinery. The aim was to evaluate the hydrolysis of WS by using liquid hot water (LHW) treatment, the detoxification of the produced wheat straw hydrolysate (WSH), and the cultivation of Trichoderma reesei using it as the only carbon source as proof of detoxification. LHW treatment was performed at 160 °C and 90 min and yielded a WSH rich in monomeric and oligomeric saccharides (~ 14 g/L) and containing degradation products in low concentration (furfural, HMF, and acetic acid). As part of the development of the extraction and detoxification strategy, we determined the specific inhibition thresholds for T. reesei for the mentioned degradation products. Detoxification was carried out by evaporation by modifying the % of volume evaporated and the pH of the solution. Approximately 55.9% of acetic acid and 100% of furfural were removed from the WSH. The fungal biomass obtained in the medium containing WSH was equivalent to 98% of the biomass obtained in the control medium.
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